In the production of windings of synchronous salient-pole electrical machine stators, especially those of hydrogenerator stators, it is customary to minimize the number of stator slots per pole per phase, therby reducing labour intensiveness and time consumption. With a small number of stator slots per pole per phase, however, the tooth harmonics in the emf curve of an electrical machine rise markedly, which results in increased energy losses, and, also, in an increased level of telephony disturbance, lying outside the limits allowed in international standards.
It is well known that in order to suppress the tooth harmonics, the poles should be distributed over the rotor rim circumference of a synchronous salient-pole electrical machine so that the distance never be the same between magnetic axes of the poles, i.e. between the lines of intersection of a cross-section plane of the rotor and longitudinal central planes, wherein magnetic fluxes generated by the poles are maximal, that is, the poles be in groups distributed in series over the rotor circumference and having an equal number of poles, whose magnetic axes within each group are spaced from each other by the same distances, equal to the distances between the magnetic axes of the poles of other groups and different from equal distances between the magnetic axes of the adjacent poles of different groups (cf., for instance, "Methods for improvement of the voltage curve and reducing the telephony disturbance ratio" by A. X. Dookshtau and G. B. Pinsky, "Electrotechnika", No. 3, 1978, pp.31-32).
Known in the art is a rotor for a synchronous salient-pole electrical machine, having a heavy rim with poles mounted thereon and evenly distributed over the circumference thereof, in which, in order to suppress the tooth harmonics, the shoes of different poles are shifted dissimilarly with respect to the cores, thereby providing a different shift of the magnetic axes of the poles with respect to symmetry axes of the cores, that is, the poles form the groups described above (cf., for instance, "Konstruktion Elektrisher Maschinen" by E. Wiedemann and W. Kellenberger, Springer-Verlag, Berlin (Heidelberg), New York, 1967, p.369, FIG. 365).
In this case, however, in order to ensure an adequate suppression of the tooth harmonics, it is necessary to have a great quantity of types of the poles of various configuration and also a great number of types of members for connection of coils and damping segments of the adjacent poles.
This complicates considerably the production of parts of the rotor of an electrical machine, as well as its assembly and repair.
There is known a rotor for a synchronous salient-pole electrical machine, having a heavy rim and poles attached by bolts thereto symmetrically with respect to their magnetic axes and unevenly distributed over the rim circumference, thus forming the groups described above, which ensures suppression of the tooth harmonics. Electrical machines provided with such rotors are installed, for example, in the Saratov's and Volkhov's hydroelectric power stations, in the Soviet Union.
In such machines, all the poles are made the same, and connecting members of two types only are required to assemble the rotor: to make connections in the intervals between adjacent poles within a group, and to make connections in the intervals between adjacent poles of different groups. Such a construction, however, can be used only with a rotor having a heavy rim, for example, all-cast or bent one, which enables the poles to be attached thereto by bolts.
The heavy-rim rotors, nevertheless, are of limited usefulness and can not be used in large-sized low-speed powerful electrical machines with the rotor of a large diameter, due to difficulties associated with the manufacturing of the rotor and its transportation. In such electrical machines rotors are used with a laminated rim having slots distributed over the circumference thereof, wherein the poles are mounted.
There is known a rotor for a synchronous salient-pole machine, having a rim built up in annular layers consisting of segments provided with recesses and mounted at a shift of the joints between the segments of each of the layers with respect to the joints between the segments of an adjacent layer so that the recesses in the segments of the adjacent layers are found to be opposite to each other, thus forming slots on the rim circumference, in which like poles are mounted, all the segments being shaped so that, in each of them, the adjacent recesses are spaced from each other by a distance equal to the rim circumference length divided by the number of the poles, so that the slots of the rim formed by the recesses, wherein the poles are mounted, are spaced from each other by the same distance equal to said distance between the adjacent recesses of the segments (cf., for instance, "Konstruktion Electrischer Maschinen" by E. Wiedemann, W. Kellenberger, Springer-Verlag Berlin (Heidelberg), New York, 1967, p.458 FIG. 429).
However, such a construction of the rotor fails to provide suppression of the tooth harmonics, since, in this case, the magnetic axes of the poles arranged on the rim circumference are found at the same distances from each other. This deteriorates the emf curve shape of the electrical machine which, as mentioned above, leads to increased energy losses and to an impermissible increase in the level of telephony disturbance.
To suppress the tooth harmonics, it could be possible to use dissimilar poles whose magnetic axes are shifted at different distances with respect to symmetry axes of the cores, for example, the poles whose shoes are dissimilarly shifted with respect to the cores as is done in electrical machines with a heavy-rim rotor. However, as mentioned above, the use of the dissimilar poles complicates considerably the manufacturing of the rotor parts as well as its assembly and repair.